This invention relates to a method and apparatus for dilating blood vessels in vasospasm.
Vasospasm is an abnormal and often persistent contraction of an artery that reduces the caliber of the artery and may critically reduce blood flow. Vasospasm can produce a partial or complete obstruction in arteries that otherwise appear completely normal. Greater or lesser amounts of dynamic or spastic constriction at the point of a fixed obstruction can create a severe reduction of flow even where the fixed obstruction itself would be clinically benign.
Vasospasm can occur spontaneously; or it may occur as the result of certain pharmacological stimuli, such as, for example, ergonovine testing; or of mechanical stimuli such as contact with a surgical instrument or a diagnostic or therapeutic catheter, for example as a complication of percutaneous transluminal catheter angioplasty (PTCA); or of environmental stimuli. Raynaud""s phenomenon and Printzmetal angina are two additional forms of vasospasm. Furthermore, certain maladies such as subarachnoid hemorrhage can also lead to vasospasm. In particular, cerebral vasospasm, which is caused by subarachnoid hemorrhage, and opthalmic artery vasospasm may cause severe consequences if not treated promptly.
Various medications have been tested for the relief of vasospasms and are only partially effective. For example, vasospasm in coronary vasculature has been treated with calcium channel blockers. However, for some unknown reason that relates to the pharmacological and anatomical differences between cerebral and coronary vasculature, these drugs are ineffective against cerebral vasospasm. In addition, mechanical treatment such as balloon angioplasty is also ineffective against cerebral vasospasm.
Other non-chemical treatments, e.g., laser irradiation-induced dilation of the vessels, of vasospasm have likewise been relatively unsuccessful or plagued with various problems. For example, laser irradiation-induced dilation of blood vessels is cumbersome, may damage surrounding healthy tissue, does not use standard catheter guide wire techniques, and provides a narrow margin between the laser energy needed to cause vasodilation and that needed to perforate the vessel wall. Moreover, in those laser techniques using low level constant wave laser radiation, vasospasm resumes as soon as the radiation ceases.
Furthermore, mechanical dilation treatments, such as balloon angioplasty, are generally ineffective because, vasospasm generally resumes after the balloon is removed, and these treatments are very difficult in arteries that are hard to catheterize, e.g., the ophthalmic artery.
This invention features dilation of blood vessels in vasospasm through the use of high frequency (on the order of microseconds) waves, e.g., hydraulic or acoustic waves, and offers several advantages over known laser irradiation- or chemical-induced dilation. These advantages include greater safety by preventing damage to the blood vessel walls by the wave generator, e.g., a laser pulse, increased maneuverability, dilation over a concentric catheter guide wire, and an increased range of energy levels that may be safely used for therapy. In addition, the invention is successful for treating cerebral vasospasm, which currently is not known to be susceptible to any mechanical or chemical treatments. Furthermore, based upon animal studies done to date, we have found that vasospasm does not resume after treatment according to the invention. The method of the invention is suitable for any vasospasm, including any vasospasm intractable to medication, either functionally, or time limited.
The invention features an apparatus for dilating a fluid-filled blood vessel in vasospasm including a catheter having a lumen containing a fluid, a wave generator arranged within the catheter lumen for generating a wave front that propagates through the fluid in the lumen and is transmitted from the distal end of the catheter to propagate through the fluid in the blood vessel, and an energy source connected to the wave generator to provide energy to produce the wave front.
The wave generator of the invention may be a laser beam, e.g., a pulse, when the energy source is a laser. In preferred embodiments, this pulse has a duration of from about 10 nanosec to about 300 xcexcsec and is of a wavelength of less than about 600 nm or greater than about 1000 nm. The laser may be, e.g., a holmium, ultra violet, or pulsed-dye visible laser.
The wave generator also may be a spark generator, ultrasound agitator, or piezoelectric agitator.
When the distal end of the catheter is open, the wave front is transmitted from the distal end of the catheter by exiting the catheter and passing into the vessel. When the distal end of the catheter is sealed with a membrane, the wave front is transmitted from the distal end of the catheter via the membrane.
In any of these embodiments, the wave may be, e.g., a hydraulic or acoustic wave.
In a preferred embodiment, the invention also features an apparatus for dilating a fluid-filled blood vessel in vasospasm that includes a catheter having a lumen containing a fluid, a laser energy conducting filament arranged axially within the catheter lumen, the distal end of the filament being positioned at a distance from the distal end of the catheter such that laser energy emitted from the filament generates a cavitation bubble within the catheter lumen that generates a wave front that propagates through the fluid in the lumen and is transmitted from the distal end of the catheter to propagate through the fluid in the blood vessel, and a laser energy source connected to the conducting filament to provide laser energy to produce the wave front.
The invention also features a method of dilating a fluid-filled blood vessel in vasospasm by propagating a wave front that induces vasodilation through a fluid in a blood vessel in need of dilation without generating a shock wave or cavitation bubble within the blood vessel.
Furthermore, the invention features a method of dilating a fluid-filled blood vessel in vasospasm by inserting a catheter into a blood vessel in vasospasm, the catheter having a-lumen containing a fluid, generating a wave front in the fluid in the catheter, propagating the wave front through the fluid in the catheter, transmitting the wave front from the distal end of the catheter, and propagating the transmitted wave front through the fluid in the blood vessel to induce vasodilation.
The wave front used in this method may be generated by a laser pulse that forms a cavitation bubble within the catheter without forming a laser breakdown-induced shock wave. In addition, the wave may be generated by other wave generators noted above.
The fluid through which the wave front propagates may be, e.g., blood, a crystalloid solution such as saline or lactated Ringer""s solution, or a colloid solution. When a laser is used, the fluid may be any solution that absorbs the incident laser energy. This fluid is in the catheter and, when it is something other than blood, may be infused into the blood vessel in vasospasm prior to dilation.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims.